# std::ranges::in_value_result

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< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
template< class I, class T > struct in_value_result; |  | (since C++23)

`ranges::in_value_result` is a class template that provides a way to store an iterator and a value as a single unit.

This class template has no base classes or declared members other than those shown below. Thus it is suitable for use with structured bindings.

All special member functions of this class template are implicitly declared, which makes specializations be aggregate classes, and propagate triviality, potentially-throwing-ness, and constexpr-ness of corresponding operations on data members.

### Template parameters

I, T | - | the types of the objects that the `ranges::in_value_result` stores.

### Data members

Member name | Definition
in | a value (that is supposed to be an iterator) of type `I`. (public member object)
value | a value (that is supposed to be a stored value) of type `T`. (public member object)

All these members are declared with `[[no_unique_address]]` attribute.

### Member functions

## std::ranges::in_value_result::operator in_value_result<I2, T2>

template<class I2, class T2> requires convertible_to<const I&, I2> && convertible_to<const T&, T2> constexpr operator in_value_result<I2, T2>() const &; | (1) |
template<class I2, class T2> requires convertible_to<I, I2> && convertible_to<T, T2> constexpr operator in_value_result<I2, T2>() &&; | (2) |

Converts *this to the result by constructing every data member of the result from the corresponding member of *this.

1) Equivalent to return {in, value};.
2) Equivalent to return {std::move(in), std::move(value)};.

### Standard library

The following standard library functions use `ranges::in_value_result` as the return type:

##### Algorithm functions
ranges::fold_left_with_iter (C++23) | left-folds a range of elements, and returns a pair (iterator, value) (algorithm function object)
ranges::fold_left_first_with_iter (C++23) | left-folds a range of elements using the first element as an initial value, and returns a pair (iterator, optional) (algorithm function object)

### Synopsis

    namespace std::ranges
    {
        template<class I, class T>
        struct in_value_result
        {
            [[no_unique_address]] I in;
            [[no_unique_address]] T value;

            template<class I2, class T2>
            requires convertible_to<const I&, I2> && convertible_to<const T&, T2>
            constexpr operator in_value_result<I2, T2>() const &
            {
                return {in, value};
            }

            template<class I2, class T2>
            requires convertible_to<I, I2> && convertible_to<T, T2>
            constexpr operator in_value_result<I2, T2>() &&
            {
                return {std::move(in), std::move(value)};
            }
        };
    }

### Notes

Each standard library algorithm that uses this family of return types declares a new alias type, e.g. using merge_result = in_in_out_result<I1, I2, O>;.

The names for such aliases are formed by adding the suffix "`_result`" to the algorithm's name. So, the return type of `std::ranges::merge` can be named as `std::ranges::merge_result`.

Unlike std::pair and std::tuple, this class template has data members of meaningful names.

### Example

Run this code

    #include <algorithm>
    #include <cassert>
    #include <functional>

    int main()
    {
        const auto v = {1, 2, 3};
        const auto ret = std::ranges::fold_left_with_iter(v, 4, std::plus<>());
        assert(ret.in == v.end());
        assert(ret.value == 1 + 2 + 3 + 4);
    }

### See also

pair | implements binary tuple, i.e. a pair of values (class template)
tuple (C++11) | implements fixed size container, which holds elements of possibly different types (class template)

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